Proof Test

Definition:
A Proof Test is a planned, periodic test carried out to detect dangerous undetected failures in a Safety Instrumented Function (SIF) or its components that are not detected during normal operation. Proof testing is critical to maintaining the designed Safety Integrity Level (SIL) of a system over time.

Proof tests can vary depending on the component and the approach by the facility.

Key Points:

  • Must be thorough enough to detect failures not caught by automatic diagnostics.
  • Proof Test Interval (TI) directly impacts the Probability of Failure on Demand (PFDavg).
  • Proof Test Coverage (Cpt) measures how effective a proof test is at detecting hidden dangerous failures.
  • Proof testing requirements should be clearly defined in the Safety Requirements Specification (SRS).

Example:
A shutdown valve is stroked and functionally tested every 12 months to verify it closes properly in response to a trip signal, thereby fulfilling its proof test requirement.

See also: Proof Test Interval (TI), Proof Test Coverage (Cpt)

Cited Source:

  • IEC 61511-1:2016, Clauses 11.9 and 16.2.

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